Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. Re. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an external electronic unit, several signal transmitting cables connecting the sensor element to the external electronic unit, a flexible tube having the cables and the sensor element disposed therein, a solid metal wire also extending inside the flexible tube, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon, examples of which can be found in the present assignee's U.S. Pat. No. 6,343,514. The connection to the external unit is accomplished via a male connector and a corresponding female connector, such that the sensor guide can be disconnected from the external unit, which, for example, allows a catheter to be threaded over the sensor guide and guided into the human or animal body. An example of a suitable external unit is described in U.S. Pat. No. 6,565,514, which is assigned to the present assignee.
For obvious reasons, the outer diameter of a sensor guide has to be relatively small; and so is, for example, the outer diameter of a sensor and guide wire assembly sold and manufactured by the present assignee under the registered trademark PressureWire® only 0.36 mm (0.014 inches) in diameter. As is well-known in the art, the solid metal wire, which can be made from stainless steel or Nitinol® and which also is called the core wire, provides the sensor guide with the necessary stiffness and torqueability. The core wire must therefore have a relatively large diameter, i.e. the core wire occupies a major portion of the available space inside the flexible tube, thereby leaving a very limited space for the signal transmitting cables. Consequently, the signal transmitting cables are very thin, and constitute delicate and sensitive parts of the sensor and guide wire assembly.
The fact that the use of such thin signal transmitting cables poses a potential problem is recognized already in the present applicant's U.S. Pat. No. 6,616,067, wherein it is pointed out that the assembly of a sensor and guide wire assembly to a large extent is a tedious and labour-intensive manual procedure which furthermore has to be executed under a microscope. Further, although different measures can be taken to protect the thin cables from being damaged, they are still sensitive parts of the sensor guide. To solve this problem, the U.S. Pat. No. 6,616,067 discloses a sensor system comprising a first electrode adapted to be in electrical contact with body tissue at a first part of a patient's body and a second electrode adapted to be in electrical contact with body tissue at a second part of the patient's body, such that the sensor system can transfer an electrical signal representing a physiological characteristic through said first and second electrodes via the body tissue. This invention utilizes the core wire to electrically connect the sensor, and the use of thin signal transmitting cables has been eliminated. However, this solution requires that electrical current flows through the patient's body, something which requires that extensive protective measures are taken to eliminate the risk that the current strength becomes too high. As the patient usually is subjected to other medical procedures, and may also be connected to other medical apparatuses, it may further be difficult to find a suitable contact site available for the connection of the second electrode.
Therefore, there remains a need for an improved way of communicating with a guide wire mounted sensor. The sensor should also be inexpensive and easy to manufacture and assemble.